The prevention of beer-spoilage by contaminating microorganisms is a major concern of commercial breweries. The predominant organisms which have been shown to spoil beer, or which have been associated with beer-spoilage are members of the genera Lactobacillus and Pediococcus (see The Prokaryotes, Vol, II, 2nd Edition, Balows, et al, Eds., 1991). These bacteria may be present in very low numbers and their detection may require three to five days or more by traditional culture methods.
Members of the genus Pediococcus are Gram-positive cocci which frequently form tetrads. They have complex nutritional requirements and are capable of fermenting a variety of sugars. They are facultative anaerobes found in a variety of habitats, most frequently associated with fermenting vegetation. There are eight species in this genus; P. damnosus is the primary member of the genus known to cause beer spoilage.
The genus Lactobacillus contains Gram-positive nonsporulating rods, utilizing strictly fermentative metabolism and having complex nutritional requirements. They are found in a variety of habitats, including water, dairy, meat and fish products, vegetation and fermenting vegetation, and in the mouth and intestinal tract of mammals.
Several studies have identified bacterial strains capable of spoiling beer, and the relative numbers of strains within the species so implicated were, in decreasing order of importance: Lactobacillus brevis, P. damnosus, L. casei, L. lindneri, L. coryniformis, L. buchneri, L. plantarum, and L. curvatus.
The current methods of detection of beer-spoilage organisms rely on classical microbiology and a general determination of the presence or absence of contamination by bacteria. These methods include: (a) culture, (b) direct fluorescence antibody (DFA), and (c) nucleic acid probes for culture confirmation. Actual identification of spoilage organisms requires classical biochemical tests and fulfillment of Koch's postulates, i.e. "reinfecting" fresh beer and showing it to become spoiled.